Induction heating of composite materials

DETAILED DESCRIPTION The present invention provides an improved apparatus and method for superplastic forming.
A preferred apparatus according to the invention comprises a die having a nonmetallic forming surface that has a shape corresponding to the desired shape for the workpiece.
Means are provided for positioning the workpiece such that it overlies the forming surface, with a first side of the workpiece facing the forming surface.
Inductive heating means are provided for subjecting the workpiece to a time varying magnetic field, such that the workpiece is heated to a temperature at which it is superplastic.
Finally, means are provided for producing a pressure differential between the first and second sides of the workpiece, while the workpiece is at said temperature, such that the workpiece deforms and assumes the shape of the forming surface.
The dies are preferably formed from a dielectric, thermally insulating material such as a castable ceramic.
Thermal energy is therefore applied to the workpiece but not the dies, leading to much shorter heating and cooling cycles as compared to the prior art technique of using resistance-type heating with metal dies.
The inductive heating means of the invention preferably comprises a plurality of electrical conductors embedded within the dies, and means for interconnecting such conductors into a coil that surrounds the workpiece.
One embodiment of the invention is an apparatus for heating a workpiece formed of a composite material susceptible to inductive heating.
The apparatus includes a die formed of a material substantially transparent to the transmission of an inductive magnetic field.
The die also includes a forming surface on which the workpiece is placed.
An inductive heater is located within the die and subjects an electrically conductive material in the composite material to an alternating magnetic field.
The alternating magnetic field heats the electrically conductive material in the composite material, thereby heating the workpiece.
In accordance with other features of the invention, the apparatus includes a plurality of electrical conductors embedded within the die